Should You Use Software-Defined Flash Storage?

"Software definition" leverages the processor's power to do things that used to require dedicated hardware. So, what does that mean for flash?

Have you noticed how everyone seems to be adding the words "software-defined" to their market term? In some cases this is just marketing gone wild. In other cases it is an appropriate description of the technology. We have software-defined storage, software-defined networking and the software-defined data center. I expect to hear to a CEO describe their entire organization as "software defined" any day now.

All this software definition is changing how technologies are developed. An excellent example is flash-based storage.

What Is Software Definition?

The use (and overuse) of the term software-defined is really about leveraging the power of the Intel CPU to do things in software that we used to do with dedicated hardware. Doing so should reduce costs and increase flexibility. As I described in my last column, "How Software-Defined Storage Impacts SSD," it can even help with adoption of hardware, like flash media and appliances.

Software-Defined Flash

The value of software definition is now working its way into the flash community and is the subject of much debate. The flash controller performs a variety of management functions that extend the life of the media and improve performance. Typically this flash intelligence is embedded as silicon or a field programmable gate array (FPGA), but now some flash vendors are starting to perform these management functions using the CPU of the host or storage system that the device is being installed on.

The upside of this method should be more rapid deployment of capabilities and functionality. It should also lead to lower development cost for the vendor. In theory this should lead to less-expensive products that are more feature rich. We have not, for the most part, seen this theory translate to reality. Most flash systems and devices that count on host CPUs to perform management functions are the same price as hardware-based flash systems and typically are at feature parity.

The other potential advantage of software-based flash management is that as you upgrade the CPU in the host you could see better flash performance. How much of this is reality is dependent on your application and whether you will actually carry your SSD investment between generations of servers as you upgrade them. In our experience this is not the case.

The downside of counting on the host CPU to execute the flash management functions is that it could impact flash and/or host performance when under stress. While the vendors that perform their flash management in hardware make a big deal about this potential problem, we have not seen a situation where it is apparent. As most IT professionals know, there is plenty of excess CPU resources in the typical data center today. Burning a few of those cycles on flash management routines should not be a major problem for most.

Should You Use Software-Defined Flash?

This is, at least right now, one of those situations where "it depends" doesn't apply. More appropriately, at least for right now, in most data centers it doesn't matter. You need to judge the flash device or storage system on its total merits. Does it deliver the performance you need, with a feature set you can live with at a price you can afford? While the advantages of hardware-based flash management or software-based management may become more apparent in the future, at least for today they are a wash.

Published: 2015-03-31The build_index_from_tree function in index.py in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a commit with a directory path starting with .git/, which is not properly handled when checking out a working tree.